The invention relates to an annular seal which has a cylindrical surface of the outside diameter DA and containing indentations, and which has a sealing lip of annular configuration made from polymeric material which is urged under resilient bias against the cylindrical surface.
An annular seal of this general kind is known. The cylindrical surface engaged by the sealing lip has indentations provided in it, which consist of grooves or ridges running parallel to one another. These grooves or ridges are formed when the cylinder surface is finished--when it is ground, for example--and can have an effect on the sealing action of the annular seal. This is especially true when the annular seal is used in connection with the sealing of a relatively rotating machine part, such as a shaft. Then, as a result of hydrodynamic effects known in themselves, axial pumping action occurs within the seal interstice, resulting in either an impairment or an improvement of the sealing action. In general it is an improvement of the sealing action that is desired. Consequently attempts have been made to establish the inclination of the individual grooves or ridges with respect to the axis of the cylindrical surface such that, in proper use, a pumping action directed towards the area to be sealed is produced in the interstice. However, this pumping action becomes increasingly apparent with increasing shaft speed, and, at very high shaft speeds, the result may be that too little of the medium being sealed remains in the gap to provide for the lubrication and cooling of the sealing lip. Premature failure of the seal is the necessary consequence.
DE-OS 21 08 341 discloses a method for the surface treatment of metallic friction surfaces, in which the friction surfaces which cooperate in their proper use are peened in whole or in part by blasting with glass beads after they are superfinished, in order to achieve a surface texture allowing good adhesion of an oil film on these surfaces while they are being run in or thereafter. The acceptable speeds in frictional engagement can thus be increased, and the saucer-like indentations produced by the glass beads can be so close together that they touch or overlap. The use of glass bead peening in connection with the production of seals is not suggested in the above-cited patent application.
It is the purpose of the invention to develop an annular seal for use in conjunction with shafts, which will be distinguished from those heretofore known by a substantially improved useful life at very high frictional speeds of more than 20 meters per second.